1. Technical Field
The present development relates to EGR routing and configuration of aftertreatment devices for a turbocharged diesel engine.
2. Background
Diesel engine exhaust is generally cooler than exhaust from a gasoline engine because the diesel engine operates with excess air and the cycle is more efficient at most operating conditions, which means there is less rejection of energy to exhaust gases. It is generally desirable to mount the turbine of the turbocharger close to the exhaust manifold so that exhaust energy, which is extracted by the turbine, is at its highest level. Turbocharger lag is partially mitigated by having the turbine located as close to the engine as possible. It is also known that exhaust aftertreatment devices, such as DOCs (diesel oxidation catalysts) and SCR (selective-catalyst reduction) catalysts, operate more efficiently when in a preferred temperature range. In particular, it is important for aftertreatment devices to attain their lightoff temperature as soon as possible following a cold start of the engine. Thus, it is desirable for quick lightoff to place aftertreatment devices as close to the engine as possible so that the aftertreatment devices can process exhaust gases soon after an engine cold start.